The present invention relates to a light scanning method of scanning a surface with a light beam emitted from a laser beam source.
There is widely known a light scanning method of scanning a surface with a light beam emitted from a laser beam source by applying the light beam through a collimator lens to a rotating light deflector, deflecting the light beam with the light deflector, and applying the deflected light beam through an f.theta. lens to the surface to be scanned.
The rotating light deflector may be a rotating polygon mirror or a pyramidal mirror. Since the light beam is deflected at a uniform angular velocity by the rotating light deflector, the f.theta. lens is necessary to scan the surface with the light beam at a constant velocity.
The f.theta. lens is also effective in focusing the deflected light beam as a light spot on the surface being scanned. Therefore, a good f.theta. lens has so-called f.theta. characteristics and curvature of field well corrected. If the curvature of field were not sufficiently corrected, the size of the light spot which scans the surface would be greatly varied dependent on the scanning position. For writing optical information, for example, the resolution of a recorded image would not be uniform in the image.
It is not necessarily easy to well correct both f.theta. characteristics and curvature of field of an f.theta. lens. An f.theta. lens which meets the desired well-corrected conditions may have problems in that the lens is of a complex arrangement and of a high cost.